Approximately 500,000 HIV-infected children are born each year in sub-Saharan Africa. Nevirapine treatment programs could prevent about half of these infections. In Arica, maternal malaria is common and frequently causes low birth weight. Important interactions between HIV and malaria infections in pregnant women have been identified ane low-cost interventions to prevent maternal materia are known. The current proposal aims to test the following hypotheses: 1. Maternal malaria increases mother-to-child transmission (MTCT) of HIV in nevirapine-treated women and children; malaria may have this effect by increasing maternal viral load, placental monocytes, and placental concentrations of TNF-alpha and CCR5; and 2. HIV-1 infections inhibit the development of pregnancy-specific anti-malarial immunity and exacerbates maternal malaria. To test these hypotheses, we will enroll approximately 1400 women at antenatal clinics in Blantyre, Malawi. HIV-positive women and their offspring will be treated with nevirapine. 400 HIV-positive women will be enrolled in a prospective cohort study in which the effects of maternal malaria. To test these hypotheses, we will enroll approximately 1400 women at antenatal clinics in Blantyre, Malawi. HIV-positive women and their offspring will be treated with nevirapine. 400 HIV-positive women will be enrolled in a prospective cohort study in which the effects of maternal malaria on HIV transmission rates will be determined. In this same group of women, we will investigate how malaria affects maternal peripheral and placental viral loads, placental histopathology, and placental and cord blood cytokine and chemokine levels. In a second substudy, the effects of HIV on pregnancy-specific antimalarial immunity (antibodies to chondroitin sulfate. A binding infected erythrocytes) will be assessed in 4 groups of 52 multigrivida (HIV+/malaria+, HIV+/malaria-). The results of this study will have important implications for designing public health program s for antenatal care in African and should promote our understanding of the pathogenesis of MTCT.